Measuring Action Potential Propagation Velocity in Murine Cortical Axons.

Measuring the action potential (AP) propagation velocity in axons is critical for understanding neuronal computation. This protocol describes the measurement of propagation velocity using a combination of somatic whole cell and axonal loose patch recordings in brain slice preparations. The axons of neurons filled with fluorescent dye via somatic whole-cell pipette can be targeted under direct optical control using the fluorophore-filled pipette.

SUMOylation of Na1.2 channels regulates the velocity of backpropagating action potentials in cortical pyramidal neurons.

Voltage-gated sodium channels located in axon initial segments (AIS) trigger action potentials (AP) and play pivotal roles in the excitability of cortical pyramidal neurons. The differential electrophysiological properties and distributions of Na1.2 and Na1.

Blood glutamate scavenging as a novel glutamate-based therapeutic approach for post-traumatic brain injury anxiety and social impairment.

Traumatic brain injury (TBI) is a serious condition that is associated with an increased risk of severe, long-term psychiatric consequences. Drugs that target the glutamatergic system have proven successful in treating both TBI and many of its psychiatric sequelae. Blood glutamate scavengers (BGS) cause a decrease in blood glutamate levels, leading to a reduction in glutamate's concentration gradient from the brain to the blood and decreased levels of brain glutamate.

Glutamate Neurotoxicity and Destruction of the Blood-Brain Barrier: Key Pathways for the Development of Neuropsychiatric Consequences of TBI and Their Potential Treatment Strategies.

Traumatic brain injury (TBI) is associated with significant cognitive and psychiatric conditions. Neuropsychiatric symptoms can persist for years following brain injury, causing major disruptions in patients' lives. In this review, we examine the role of glutamate as an aftereffect of TBI that contributes to the development of neuropsychiatric conditions.

Frequency- and spike-timing-dependent mitochondrial Ca signaling regulates the metabolic rate and synaptic efficacy in cortical neurons.

Mitochondrial activity is crucial for the plasticity of central synapses, but how the firing pattern of pre- and postsynaptic neurons affects the mitochondria remains elusive. We recorded changes in the fluorescence of cytosolic and mitochondrial Ca indicators in cell bodies, axons, and dendrites of cortical pyramidal neurons in mouse brain slices while evoking pre- and postsynaptic spikes. Postsynaptic spike firing elicited fast mitochondrial Ca responses that were about threefold larger in the somas and apical dendrites than in basal dendrites and axons.

Subcellular Distribution of Persistent Sodium Conductance in Cortical Pyramidal Neurons.

Cortical pyramidal neurons possess a persistent Na current ( ), which, in contrast to the larger transient current, does not undergo rapid inactivation. Although relatively quite small, is active at subthreshold voltages and therefore plays an important role in neuronal input-output processing. The subcellular distribution of channels responsible for and the mechanisms that render them persistent are not known.

Aberrant activity of mitochondrial NCLX is linked to impaired synaptic transmission and is associated with mental retardation.

Calcium dynamics control synaptic transmission. Calcium triggers synaptic vesicle fusion, determines release probability, modulates vesicle recycling, participates in long-term plasticity and regulates cellular metabolism. Mitochondria, the main source of cellular energy, serve as calcium signaling hubs.

Dynamic Gain Analysis Reveals Encoding Deficiencies in Cortical Neurons That Recover from Hypoxia-Induced Spreading Depolarizations.

Cortical regions that are damaged by insults, such as ischemia, hypoxia, and trauma, frequently generate spreading depolarization (SD). At the neuronal level, SDs entail complete breakdown of ionic gradients, persisting for seconds to minutes. It is unclear whether these transient events have a more lasting influence on neuronal function.

Role of sodium channel subtype in action potential generation by neocortical pyramidal neurons.

Neocortical pyramidal neurons express several distinct subtypes of voltage-gated Na channels. In mature cells, Na1.6 is the dominant channel subtype in the axon initial segment (AIS) as well as in the nodes of Ranvier.

M-current inhibition rapidly induces a unique CK2-dependent plasticity of the axon initial segment.

Alterations in synaptic input, persisting for hours to days, elicit homeostatic plastic changes in the axon initial segment (AIS), which is pivotal for spike generation. Here, in hippocampal pyramidal neurons of both primary cultures and slices, we triggered a unique form of AIS plasticity by selectively targeting M-type K channels, which predominantly localize to the AIS and are essential for tuning neuronal excitability. While acute M-current inhibition via cholinergic activation or direct channel block made neurons more excitable, minutes to hours of sustained M-current depression resulted in a gradual reduction in intrinsic excitability.

Optogenetic control of mitochondrial metabolism and Ca signaling by mitochondria-targeted opsins.

Key mitochondrial functions such as ATP production, Ca uptake and release, and substrate accumulation depend on the proton electrochemical gradient (ΔμH) across the inner membrane. Although several drugs can modulate ΔμH, their effects are hardly reversible, and lack cellular specificity and spatial resolution. Although channelrhodopsins are widely used to modulate the plasma membrane potential of excitable cells, mitochondria have thus far eluded optogenetic control.

The earliest neuronal responses to hypoxia in the neocortical circuit are glutamate-dependent.

Soon after exposure to hypoxia or ischemia, neurons in cortical tissues undergo massive anoxic depolarization (AD). This precipitous event is preceded by more subtle neuronal changes, including enhanced excitatory and inhibitory synaptic transmitter release. Here, we have used patch-in-slice techniques to identify the earliest effects of acute hypoxia on the synaptic and intrinsic properties of Layer 5 neurons, to determine their time course and to evaluate the role of glutamate receptors in their generation.

Functional implications of axon initial segment cytoskeletal disruption in stroke.

Axon initial segment (AIS) is the proximal part of the axon, which is not covered with a myelin sheath and possesses a distinctive, specialized assembly of voltage-gated ion channels and associated proteins. AIS plays critical roles in synaptic integration and action potential generation in central neurons. Recent evidence shows that stroke causes rapid, irreversible calpain-mediated proteolysis of the AIS cytoskeleton of neurons surrounding the ischemic necrotic core.

The Outwardly Rectifying Current of Layer 5 Neocortical Neurons that was Originally Identified as "Non-Specific Cationic" Is Essentially a Potassium Current.

In whole-cell patch clamp recordings from layer 5 neocortical neurons, blockade of voltage gated sodium and calcium channels leaves a cesium current that is outward rectifying. This current was originally identified as a "non-specific cationic current", and subsequently it was hypothesized that it is mediated by TRP channels. In order to test this hypothesis, we used fluorescence imaging of intracellular sodium and calcium indicators, and found no evidence to suggest that it is associated with influx of either of these ions to the cell body or dendrites.

Differential TGF-β Signaling in Glial Subsets Underlies IL-6-Mediated Epileptogenesis in Mice.

TGF-β1 is a master cytokine in immune regulation, orchestrating both pro- and anti-inflammatory reactions. Recent studies show that whereas TGF-β1 induces a quiescent microglia phenotype, it plays a pathogenic role in the neurovascular unit and triggers neuronal hyperexcitability and epileptogenesis. In this study, we show that, in primary glial cultures, TGF-β signaling induces rapid upregulation of the cytokine IL-6 in astrocytes, but not in microglia, via enhanced expression, phosphorylation, and nuclear translocation of SMAD2/3.

Long-term GnRH-induced gonadotropin secretion in a novel hypothalamo-pituitary slice culture from tilapia brain.

Organotypic cultures, prepared from hypothalamo-pituitary slices of tilapia, were developed to enable long-term study of secretory cells in the pituitary of a teleost. Values of membrane potential at rest were similar to those recorded from acute slices, and cells presented similar spontaneous spikes and spikelets. Some cells also exhibited slow spontaneous oscillations in membrane potential, which may be network-driven.

Imaging sodium in axons and dendrites.

This protocol describes a one-photon method to detect the time course and the spatial distribution of intracellular sodium ion concentrations [Na(+)](i), which result from action potentials and synaptic activity in different regions of neurons in brain slices. The one-photon technique has been applied to several different cell types and can likely be applied to other neurons in brain slices, particularly those that are relatively flat. Imaging of [Na(+)](i) changes is much less common than imaging of [Ca(2+)](i) changes, in part because typical signals are much smaller and more difficult to detect.

Spatial mismatch between the Na+ flux and spike initiation in axon initial segment.

It is widely believed that, in cortical pyramidal cells, action potentials (APs) initiate in the distal portion of axon initial segment (AIS) because that is where Na(+) channel density is highest. To investigate the relationship between the density of Na(+) channels and the spatiotemporal pattern of AP initiation, we simultaneously recorded Na(+) flux and action currents along the proximal axonal length. We found that functional Na(+) channel density is approximately four times lower in the AP trigger zone than in the middle of the AIS, where it is highest.

Upregulation of KCC2 activity by zinc-mediated neurotransmission via the mZnR/GPR39 receptor.

Vesicular Zn(2+) regulates postsynaptic neuronal excitability upon its corelease with glutamate. We previously demonstrated that synaptic Zn(2+) acts via a distinct metabotropic zinc-sensing receptor (mZnR) in neurons to trigger Ca(2+) responses in the hippocampus. Here, we show that physiological activation of mZnR signaling induces enhanced K(+)/Cl(-) cotransporter 2 (KCC2) activity and surface expression.

Na+ imaging reveals little difference in action potential-evoked Na+ influx between axon and soma.

In cortical pyramidal neurons, the axon initial segment (AIS) is pivotal in synaptic integration. It has been asserted that this is because there is a high density of Na(+) channels in the AIS. However, we found that action potential-associated Na(+) flux, as measured by high-speed fluorescence Na(+) imaging, was about threefold larger in the rat AIS than in the soma.

Endogenous polyamines regulate cortical neuronal excitability by blocking voltage-gated Na+ channels.

Because the excitable properties of neurons in the neocortex depend on the characteristics of voltage-gated Na(+) channels, factors which regulate those characteristics can fundamentally modify the dynamics of cortical circuits. Here, we report on a novel neuromodulatory mechanism that links the availability of Na(+) channels to metabolism of polyamines (PAs) in the cerebral cortex. Using single channel and whole-cell recordings, we found that products of PA metabolism, the ubiquitous aliphatic polycations spermine and spermidine, are endogenous blockers of Na(+) channels in layer 5 pyramidal cells.

Bolus injection of acetylcholine terminates atrial fibrillation in rats.

It is well established that a tonic increase in the availability of the atrial muscarinic K(+) channels, either by enhanced vagal tone or by steady infusion of a low-dose of cholinergic or adenosine receptor agonists, promotes the genesis of atrial fibrillation. Here, we aimed to test the hypothesis that bolus administration of a muscarinic receptor agonist would destabilize and terminate atrial arrhythmia by uniformly and transiently activating K(+) channels throughout the atria, and that if the agonist was rapidly hydrolysable, it would dissipate before the more tonic, pro-arrhythmic effects could take hold. The episodes of untreated atrial fibrillation, induced in anesthetized rats by programmed electrical stimulation via trans-esophageal bipolar catheter, lasted on average 8.